Pololu A-Star 32U4 Robot Controller User’s Guide...A-Star 32U4 Robot Controller with Raspberry Pi...
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Pololu A-Star 32U4 Robot Controller User’s Guide Pololu A-Star 32U4 Robot Controller User’s Guide © 2001–2019 Pololu Corporation https://www.pololu.com/docs/0J66/all Page 1 of 50
Transcript of Pololu A-Star 32U4 Robot Controller User’s Guide...A-Star 32U4 Robot Controller with Raspberry Pi...
Pololu A-Star 32U4 RobotController User’s Guide
Pololu A-Star 32U4 Robot Controller User’s Guide © 2001–2019 Pololu Corporation
https://www.pololu.com/docs/0J66/all Page 1 of 50
1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Supported operating systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2. Contacting Pololu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3. A-Star 32U4 Robot Controller with Raspberry Pi Bridge . . . . . . . . . . . . . . . . . . . . . . 8
3.1. Microcontroller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.2. User interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.3. LV motor drivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.4. SV motor drivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.5. Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.6. LV regulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.7. SV regulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.8. Raspberry Pi interface and level shifters . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.9. Pinout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.10. Pin assignments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.11. AVR Timers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.12. Schematics and dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
4. Getting started . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
4.1. Installing Windows drivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
4.2. Programming using the Arduino IDE . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
4.3. Programming using avr-gcc and AVRDUDE . . . . . . . . . . . . . . . . . . . . . . . 37
5. A-Star 32U4 Arduino library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
6. The A-Star 32U4 USB interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
7. The A-Star 32U4 Bootloader . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
8. Reviving an unresponsive A-Star . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
8.1. Reviving using the Arduino IDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
8.2. Reviving using AVRDUDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
9. Related resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
Pololu A-Star 32U4 Robot Controller User’s Guide © 2001–2019 Pololu Corporation
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A-Star 32U4 Robot Controller LV with RaspberryPi Bridge (SMT components only).
A-Star 32U4 Robot Controller SV with RaspberryPi Bridge (SMT components only).
1. Overview
The Pololu A-Star 32U4 Robot Controller with
Raspberry Pi Bridge is a programmable module
designed to be the core of a small robot, either
as an auxiliary controller atop a Raspberry Pi
base or as a complete control solution on its
own.
At its heart is an Atmel ATmega32U4 AVR
microcontroller, which has 32 KB of flash
program memory, 2.5 KB of RAM, and built-in
USB functionality. The controller adds a
complement of peripheral hardware useful for
robotics applications, including dual H-bridge
motor drivers capable of delivering at least 1.7 A
per channel continuously, as well as an efficient
switching voltage regulator and level shifters that
enable it to power and communicate with a
Raspberry Pi.
This A-Star is available in two versions with
different operating voltage ranges: the Robot
Controller LV (blue solder mask) accepts a 2.7 V
to 11 V input voltage, and the Robot Controller
SV (green solder mask) accepts a 5.5 V to 36 V
input voltage.
Like other A-Star programmable controllers
[https://www.pololu.com/category/149/a-star-
programmable-controllers] (abbreviated A*), the
robot controller features a USB interface and ships with a preloaded Arduino-compatible bootloader.
We provide a software add-on that enables it to be easily programmed from the Arduino environment,
as well as an Arduino library to help interface with its on-board hardware.
A USB A to Micro-B cable [https://www.pololu.com/product/2072] (not included) is required
to connect the A-Star 32U4 Robot Controller to a computer.
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1. Overview Page 3 of 50
Features
• Dimensions: 65 mm × 56 mm (2.6″ × 2.2″)
• Programmable ATmega32U4 MCU with 32 KB flash, 2.5 KB SRAM, 1 KB EEPROM, and
native full-speed USB (clocked by precision 16 MHz crystal oscillator)
• Preloaded with Arduino-compatible bootloader (no external programmer required)
• All 26 general-purpose I/O lines from the ATmega32U4 are broken out (including PB0, PD5,
and PE2); 7 of these can be used as hardware PWM outputs and 12 of these can be used as
analog inputs (some I/O lines are used by on-board hardware)
• Convenient 0.1″-spaced power, ground, and signal connection points
• Dual bidirectional motor drivers (≥1.7 A per channel)
• Buzzer option for simple sounds and music
• 3 user-controllable LEDs
• 3 user pushbuttons
• Reset button
• Level shifters for interfacing 5 V logic to 3.3 V Raspberry Pi
• Power features:
◦ 5 V power can be sourced from USB or from external supply through on-board
regulator (with several access points for connecting external power)
▪ LV: 2.7 V to 11 V input
▪ SV: 5.5 V to 36 V input
◦ Switching 5 V regulator enables efficient operation
◦ Power switch for external power inputs
◦ Reverse-voltage protection on external power inputs
◦ Power selection circuit allows for seamless switching between power sources while
providing overcurrent protection, and feedback about which power source is
selected
◦ Provides 5 V power to Raspberry Pi
• 6-pin ISP header for use with an external programmer [https://www.pololu.com/product/3172]
Pololu A-Star 32U4 Robot Controller User’s Guide © 2001–2019 Pololu Corporation
1. Overview Page 4 of 50
A-Star comparison table
A-Star 328PBMicro
A-Star 32U4Micro
A-Star 32U4 MiniULV
A-Star 32U4 MiniLV
A-Star 32U4 MiniSV
A-Star 32U4Prime LV
A-Star 32U4Prime SV
A-Star 32U4 RobotController LV
A-Star 32U4 RobotController SV
Microcontroller: ATmega328PB ATmega32U4
User I/O lines: 24 18 26 26(1) 26(1)
PWM outputs: 9 7 7 7 7(1)
Analog inputs: 8 8 12 12 12(1)
Ground accesspoints: 6 2 4 43 44
User LEDs: 1 2 3 3 3
Userpushbuttons: — — — 3 3
USB interface:
Reset button:
Power switch:
Buzzer option:
microSD option:
LCD option:
Motor drivers:
Operatingvoltage:
3.3V VCC: 3.8 V to15 V
5V VCC: 5.5 V to15 V
5.5 V to 15 V
ULV: 0.5 V to5.5 V
LV: 2.7 V to 11.8 VSV: 5 V to 40 V
LV: 2 V to 16 VSV: 5 V to 36 V
LV: 2.7 V to 11 VSV: 5.5 V to 36 V
Regulator type: 3.3 V or 5 V linear 5 V linear
5 V switching
ULV: step-upLV: step-up/step-
downSV: step-down
5 V switching
LV: step-up/step-down
SV: step-down
5 V switching
LV: step-up/step-downSV: step-down
Regulated
current:(2) 100 mA 100 mAULV: 500 mA
LV: 1 ASV: 800 mA
LV: 1.8 ASV: 1 A
LV: 1 ASV: 1.5 A
Dimensions: 1.3″ × 0.7″ 1″ × 0.6″ 1.9″ × 0.7″ 2.8″ × 2.1″ 2.6″ × 2.2″
Weight: 1.5 g(3) 1.3 g(3) 3.4 g(3) 13 g to 33 g 14 g to 23 g
1 Some microcontroller resources are used by on-board hardware.2 These values are rough approximations for comparison purposes. Available current depends on input voltage, current consumedby the board, ambient conditions, and regulator topology. See product documentation and performance graphs for details.3 Without included optional headers.
Pololu A-Star 32U4 Robot Controller User’s Guide © 2001–2019 Pololu Corporation
1. Overview Page 5 of 50
1.1. Supported operating systems
The A-Star 32U4 Robot Controller can be programmed using any operating system that supports the
Arduino environment. We have tested the A-Stars, our Arduino software add-on, and the Arduino IDE
on Microsoft Windows 10, 8.1, 8, 7, Vista, XP (with Service Pack 3), Linux, and Mac OS X.
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1. Overview Page 6 of 50
2. Contacting PololuWe would be delighted to hear from you about any of your projects and about your experience with
the Pololu A-Star Robot Controller. You can contact us [https://www.pololu.com/contact] directly or post
on our forum [http://forum.pololu.com/]. Tell us what we did well, what we could improve, what you would
like to see in the future, or anything else you would like to say!
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2. Contacting Pololu Page 7 of 50
3. A-Star 32U4 Robot Controller with Raspberry Pi Bridge
3.1. Microcontroller
Like other A-Star 32U4 programmable controllers [https://www.pololu.com/category/149/a-star-
programmable-controllers], the A-Star 32U4 Robot Controller features an integrated, USB-enabled
ATmega32U4 AVR microcontroller from Atmel, clocked by a precision 16 MHz crystal oscillator. This
is the same microcontroller and clock frequency used in the Arduino Leonardo [https://www.pololu.com/
product/2192] and Micro [https://www.pololu.com/product/2188].
The board includes a USB Micro-B connector that can be used to connect to a computer’s USB port
via a USB A to Micro-B cable [https://www.pololu.com/product/2072] (not included). The USB connection
can be used to transmit and receive data from the computer and program the board over USB. The
USB connection can also provide power for the microcontroller and most of the other hardware on the
A-Star (but not motor power); see Section 3.5 for more details.
The robot controller’s ATmega32U4 comes preloaded with the Arduino-compatible A-Star 32U4
USB bootloader [https://www.pololu.com/docs/0J66/7], which allows it to be easily programmed using the
Arduino IDE. For more information about programming the A-Star 32U4 Robot Controller, see Section
4.
The board also has a 6-pin ISP header that allows it to be programmed with an external programmer,
such as our USB AVR programmer [https://www.pololu.com/product/3172]. Pin 1 of the header is indicated
with a small white dot and has an octagonal shape.
3.2. User interface
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LEDs
The A-Star 32U4 Robot Controller has five indicator LEDs.
• A yellow user LED is connected to Arduino digital pin 13, or PC7. You can drive this pin high
in a user program to turn this LED on. The A-Star 32U4 Bootloader [https://www.pololu.com/
docs/0J61/9] fades this LED on and off while it is waiting for a sketch to be loaded.
• A green user LED is connected to PD5 and lights when the pin is driven low. While the board
is running the A-Star 32U4 Bootloader or a program compiled in the Arduino environment, it
will flash this LED when it is transmitting data via the USB connection.
• A red user LED is connected to Arduino pin 17, or PB0, and lights when the pin is driven low.
While the board is running the A-Star 32U4 Bootloader or a program compiled in the Arduino
environment, it will flash this LED when it is receiving data via the USB connection.
The AStar32U4 library contains functions that make it easier to control the three user LEDs. The green
and red user LEDs also share I/O lines with pushbuttons (see below).
• A blue power LED next to the power switch indicates when the controller is receiving power
from an external power source connected to the Power In terminals (the power switch must
be turned on).
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• A green power LED on the left edge of the board near the USB connector indicates when the
USB bus voltage (VBUS) is present.
Pushbuttons
The A-Star 32U4 Robot Controller has four pushbuttons: a reset button on the right edge and three
user pushbuttons located along the bottom edge of the main board. The user pushbuttons, labeled
A, B, and C, are on Arduino pin 14 (PB3), PD5, and Arduino pin 17 (PB0), respectively. Pressing one
of these buttons pulls the associated I/O pin to ground through a resistor.
The three buttons’ I/O lines are also used for other purposes: pin 14 is MISO on the SPI interface,
and PD5 and pin 17 control the green and red user LEDs. Although these uses require the pins to be
driven by the AVR (or SPI slave devices in the case of MISO), resistors in the button circuits ensure
that the A* will not be damaged even if the corresponding buttons are pressed at the same time, nor
will SPI communications be disrupted. The functions in the AStar32U4 library take care of configuring
the pins, reading and debouncing the buttons, and restoring the pins to their original states.
Buzzer
The assembled version of the A-Star 32U4 Robot Controller features a buzzer [https://www.pololu.com/
product/1484] that can be used to generate simple sounds and music. The buzzer is not present on the
SMT-only version, but the buzzer driver circuit is still populated, allowing you to solder in your own
buzzer or speaker.
A through-hole jumper next to the buzzer provides a way to connect the buzzer input, labeled Buzzer,
to digital pin 6 (which also serves as OC4D, a hardware PWM output from the AVR’s 10-bit Timer4).
If you alternate between driving the buzzer pin high and low at a given frequency, the buzzer will
produce sound at that frequency. You can play notes and music with the buzzer using functions in the
AStar32U4 library.
3.3. LV motor drivers
The A-Star 32U4 Robot Controller LV features two Texas Instruments DRV8838 motor drivers that
can each deliver a continuous 1.8 A. The motor power supply is derived from an external source
connected to the A-Star’s Power In terminals, which also feeds the on-board voltage regulator and
should have a voltage between 2.7 V and 11 V. (Although the DRV8838 works with motor supply
voltages as low as 0 V, the voltage regulator requires a minimum input voltage of 2.7 V.) For more
information about the drivers, see the DRV8838 datasheet [https://www.pololu.com/file/0J806/drv8838.pdf]
(1MB pdf). (We also sell a standalone carrier board [https://www.pololu.com/product/2990] for this motor
driver.)
The motor driver outputs, together with power pins, are connected to sets of through-holes along
the left side of the board. The larger holes are designed for 3.5 mm screw terminal blocks
Pololu A-Star 32U4 Robot Controller User’s Guide © 2001–2019 Pololu Corporation
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[https://www.pololu.com/product/2444], which are soldered in on the assembled version. Alternatively, 0.1″
headers [https://www.pololu.com/product/965] can be used with the smaller holes on the SMT-only version,
or motor wires can be soldered directly to either set of holes.
Driving motors with an A-Star 32U4 Robot Controller LV with Raspberry Pi Bridge on aRaspberry Pi Model B+ or Pi 2 Model B.
Although the LV and SV versions of the robot controller use different driver ICs, the motor driver
interface is identical between the two versions. Four pins are used to control the drivers:
• Digital pin 12, or PD6, controls the direction of motor 1 (when LOW, motor current flows
from A to B; when HIGH, current flows from B to A).
• PE2 (which does not have an Arduino pin number) controls the direction of motor 2.
• Digital pin 9, or PB5, controls the speed of motor 1 with PWM (pulse width modulation)
generated by the ATmega32U4’s Timer1.
• Digital pin 10, or PB6, controls the speed of motor 2 with PWM.
The AStar32U4 library provides functions that allow you to easily control the motors.
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Maximum current and power dissipation considerations
The DRV8838 datasheet recommends a maximum continuous current of 1.8 A, and the robot
controller’s printed circuit board typically draws enough heat out of the motor driver chips to allow it to
sustain this amount of current. In our tests, we found that the chip was able to deliver 1.8 A for many
minutes without triggering a thermal shutdown. Our tests were conducted at 100% duty cycle with no
forced air flow; PWMing the motor will introduce additional heating proportional to the frequency.
Motor currents over 1.8 A will likely trip either the over-temperature or over-current protection of the
DRV8838. The current limiting threshold can be as low as 1.9 A or as high as 3.5 A. This limiting helps
prevent damage to the drivers if a motor draws too much current, although the reduced current output
will degrade motor performance.
Some situations can increase heating of the motor drivers and reduce their maximum available current
output, such as drawing a large amount of current from the A-Star’s 5 V regulator, mounting the board
on a Raspberry Pi, or using it in an enclosure that limits air flow. The actual current you can deliver will
depend on how well you can keep the motor drivers cool.
This product can get hot enough to burn you long before the chip overheats. Take care
when handling this product and other components connected to it.
3.4. SV motor drivers
The A-Star 32U4 Robot Controller SV features two Maxim MAX14870 motor drivers that can each
deliver a continuous 1.7 A (2.5 A peak). The motor power supply is derived from an external source
connected to the A-Star’s Power In terminals, which also feeds the on-board voltage regulator and
should have a voltage between 5.5 V and 36 V. (Although the MAX14870 works with motor supply
voltages as low as 4.5 V, the voltage regulator requires a minimum input voltage of 5.5 V.) For
more information about the drivers, see the MAX14870 datasheet [https://www.pololu.com/file/0J885/
MAX14870.pdf] (492k pdf). (We also sell a standalone carrier board [https://www.pololu.com/product/2961]
for this motor driver.)
The motor driver outputs, together with power pins, are connected to sets of through-holes along
the left side of the board. The larger holes are designed for 3.5 mm screw terminal blocks
[https://www.pololu.com/product/2444], which are soldered in on the assembled version. Alternatively, 0.1″
headers [https://www.pololu.com/product/965] can be used with the smaller holes on the SMT-only version,
or motor wires can be soldered directly to either set of holes.
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Driving motors with an A-Star 32U4 Robot Controller SV with Raspberry Pi Bridge on aRaspberry Pi Model B+ or Pi 2 Model B.
Although the LV and SV versions of the robot controller use different driver ICs, the motor driver
interface is identical between the two versions. Four pins are used to control the drivers:
• Digital pin 12, or PD6, controls the direction of motor 1 (when LOW, motor current flows
from A to B; when HIGH, current flows from B to A).
• PE2 (which does not have an Arduino pin number) controls the direction of motor 2.
• Digital pin 9, or PB5, controls the speed of motor 1 with PWM (pulse width modulation)
generated by the ATmega32U4’s Timer1.
• Digital pin 10, or PB6, controls the speed of motor 2 with PWM.
The AStar32U4 library provides functions that allow you to easily control the motors.
Maximum current and power dissipation considerations
The MAX14870 datasheet recommends a maximum current of 2.5 A. However, the chip by itself will
typically overheat at lower currents. In our tests, we found that the chip was able to deliver 2.5 A for
only a few seconds before the chip’s thermal protection kicked in and disabled the motor outputs; a
continuous current of 1.7 A was sustainable for many minutes without triggering a thermal shutdown.
Our tests were conducted at 100% duty cycle with no forced air flow; PWMing the motor will introduce
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additional heating proportional to the frequency.
Some situations can increase heating of the motor drivers and reduce their maximum available current
output, such as drawing a large amount of current from the A-Star’s 5 V regulator, mounting the board
on a Raspberry Pi, or using it in an enclosure that limits air flow. The actual current you can deliver
will depend on how well you can keep the motor driver cool. The MAX14870 also has over-current
protection that triggers when the output current exceeds a certain limit (3 A minimum), which can help
prevent damage to the drivers if a motor draws too much current.
This product can get hot enough to burn you long before the chip overheats. Take care
when handling this product and other components connected to it.
3.5. Power
The A-Star 32U4 Robot Controller can be powered from an external voltage source, which is regulated
to 5 V by its on-board switching regulator; the provided voltage is also used to supply the motor drivers
directly. Alternatively, the A-Star’s USB connector can be used to provide 5 V only, leaving the motor
drivers unpowered.
An external supply should be be connected to the points labeled Power In (or PWR+ and GND).
These are power inputs with reverse-voltage protection that are controlled by the power switch.
Together with the motor outputs, these power inputs are connected to sets of through-holes along
the left side of the board. The larger holes are designed for 3.5 mm screw terminal blocks
[https://www.pololu.com/product/2444], while the smaller ones can be used with 0.1″ headers
[https://www.pololu.com/product/965]. A DC barrel jack [https://www.pololu.com/product/1139] can also be
used to provide power. On the assembled version of the board, a six-pin strip of 3.5 mm terminal
blocks and a barrel jack are soldered in for motor and power connections.
Warning: You must never connect different power sources to multiple Power In locations at
the same time, as doing so will create a short between the supplies.
The slide switch on the A* controls whether the external source is connected to the 5 V regulator and
motor drivers, providing a convenient way to switch off external power to the robot controller (and
optionally an attached Raspberry Pi) without unplugging any connections. The adjacent set of three
pins provides a place to connect your own power switch: to enable external power, connect the middle
pin to ground (accessible through the pin on the right).
When power is supplied through the Power In pins, the VIN pins can be used as an output to
supply reverse-protected and switched power to other devices. Alternatively, the external supply can
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be connected directly between VIN and GND, bypassing the reverse-voltage protection and power
switch.
One of the positive power inputs, labeled (PWR+), can optionally be reconfigured to serve as a
VIN access point instead. To do so, cut the surface-mount jumper on the underside of the board to
disconnect the PWR+ pad and the center pad, then use solder to bridge the VIN pad and the center
pad.
In a battery-powered application, it might be useful for the A-Star to monitor the battery’s voltage level.
The BATLEV pin provides access to a voltage divider that outputs one-third of the VIN voltage, and
this voltage can be read by connecting it to the adjacent analog pin 1 (A1) (or another analog input).
The readBatteryMillivoltsLV() and readBatteryMillivoltsSV() functions in the AStar32U4 library
can be used to determine the battery voltage from this reading.
5V regulator
VIN supplies power to a 5 V regulator, whose output is designated VREG. The allowable input voltage
range depends on the particular version of the A-Star 32U4 Robot Controller:
• LV: 2.7 V to 11 V (see Section 3.6 for regulator details)
• SV: 5.5 V to 36 V (see Section 3.7 for regulator details)
The regulator can be disabled by driving the regulator shutdown pin, REGSHDN, high; this will cause
5 V power to be sourced from USB instead if it is available.
Power selection
The A-Star 32U4 Robot Controller’s power selection circuit uses the TPS2113A power multiplexer
[https://www.pololu.com/product/2596] from Texas Instruments to choose whether its 5 V supply
(designated 5V) is sourced from USB or an external supply via the regulator, allowing both sources to
be connected at the same time and enabling the A* to safely and seamlessly transition between them.
The TPS2113A is configured to select external power unless the regulator output falls below about
4.5 V. If this happens, it will select the higher of the two sources, which will typically be the USB 5 V
bus voltage if the A* is connected to USB.
Consequently, when the A-Star is connected to a computer via USB, it will receive 5 V logic power
even when the power switch is off. This can be useful if you want to upload or test a program without
drawing power from batteries and without operating motors. It is safe to have USB connected and
external power switched on at the same time.
The currently selected source is indicated by the STAT pin in the middle of the board; this pin is
an open-drain output that is low if the external power source is selected and high-impedance if the
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USB supply is selected. The current limit of the TPS2113A is set to about 1.9 A nominally. For more
information about the power multiplexer, see the TPS2113A datasheet [https://www.pololu.com/file/0J771/
tps2113a.pdf] (1MB pdf).
Raspberry Pi power
By default, the robot controller will provide power from its 5V line to an attached Raspberry Pi. In this
situation, we recommend supplying external power through the Power In pins so that the Raspberry
Pi receives power from the A-Star’s on-board switching regulator. Alternatively, you can use a USB
wall power adapter [https://www.pololu.com/product/1459] to supply power through the A-Star’s USB
connector, although we have sometimes observed AVR brown-out resets occurring when the controller
is powering the Raspberry Pi this way. A typical computer USB port might not be able to supply enough
current to properly power the A-Star and an attached Raspberry Pi.
Power provided to the Raspberry Pi can be switched off by driving the Raspberry Pi shutdown pin,
RPISHDN, to 5 V.
An ideal diode circuit on the A* makes it safe to have a different power supply connected to the
Raspberry Pi (for example, through the Raspberry Pi’s USB Micro-B receptacle) while the A-Star 32U4
Robot Controller is connected and powered. (In other words, it is safe to have any combination of A-
Star USB power, A-Star external power, and Raspberry Pi USB power connected to the system.) The
RPI5V pin provides direct access to the Raspberry Pi’s 5 V line, which will typically come from the
higher of the two power sources.
Note that the diode circuit prevents power from being shared in the reverse direction: the Raspberry
Pi cannot supply 5 V logic power to the robot controller through the 40-pin connector.
3.3V supply for level shifters
Some of the level shifters on the A-Star are supplied with 3.3 V provided by an attached Raspberry
Pi, and this voltage is also accessible through the RPI3V3 pins. If you want to use the level shifters
in an application without a Raspberry Pi, you can instead supply them from the ATmega32U4
microcontroller’s integrated 3.3 V regulator by connecting the AVR3V3 pin to the adjacent RPI3V3 pin.
(It is preferable to use the Raspberry Pi’s 3.3 V supply when available because it is produced by a
switching regulator that is more efficient and can provide more current than the linear regulator in the
AVR.) Alternatively, you can supply a different voltage between 1.65 V and 5 V to the RPI3V3 pin to
make the level shifters shift to that voltage instead. See Section 3.8 for information about the level
shifters.
3.6. LV regulator
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The A-Star 32U4 Robot Controller LV can be
powered from a 2.7 V to 11 V external source. The
input voltage is regulated to 5 V by a TPS63061
switching step-up/step-down (buck-boost) converter
from Texas Instruments; although the regulator itself
works with input voltages up to 11.8 V, the motor
drivers limit the robot controller’s maximum input
voltage to 11 V. (We also make a standalone
regulator [https://www.pololu.com/product/2123] based on
this integrated circuit.)
The regulator’s flexibility in input voltage is especially
well-suited for battery-powered applications in which the battery voltage begins above 5 V and drops
below 5 V as the battery discharges. Without the typical restriction on the battery voltage staying
above 5 V throughout its life, a wider range of battery types can be considered. For example:
• A 4-cell battery holder, which might have a 6 V output with fresh alkalines or a 4.0 V output
with partially discharged NiMH cells, can be used to power this A*.
• A disposable 9 V battery powering the board can be discharged to under 3 V instead of
cutting out at 6 V, as with typical linear or step-down regulators.
As shown in the left graph below, the LV’s switching regulator has an efficiency – defined as
(Power out)/(Power in) – of 80% to 90% for most combinations of input voltage and load.
The A-Star’s components, including the microcontroller and LEDs, draw 30 mA to 40 mA in typical
applications (without the buzzer). The rest of the regulator’s achievable output current, which depends
on input voltage as well as ambient conditions, can be used to power other devices; this can include an
attached Raspberry Pi (which typically draws a few hundred milliamps). The right graph above shows
output currents at which the voltage regulator’s over-temperature protection typically kicks in after a
few seconds. These currents represent the limit of the regulator’s capability and cannot be sustained
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for long periods; under typical operating conditions, a safe limit for the maximum continuous regulator
output current is 60% to 70% of the values shown in the graph.
3.7. SV regulator
The A-Star 32U4 Robot Controller SV can be
powered from a 5.5 V to 36 V external source. The
input voltage is regulated to 5 V by an MP4423H
switching step-down (buck) converter from Monolithic
Power Systems. (We also make a standalone
regulator [https://www.pololu.com/product/2858] based on
this integrated circuit.)
As shown in the left graph below, the SV’s switching
regulator has an efficiency – defined as
(Power out)/(Power in) – of 80% to 95% for most
combinations of input voltage and load.
The A-Star’s components, including the microcontroller and LEDs, draw 30 mA to 40 mA in typical
applications (without the buzzer). The rest of the regulator’s achievable output current, which depends
on input voltage as well as ambient conditions, can be used to power other devices; this can include
an attached Raspberry Pi (which typically draws a few hundred milliamps). The right graph above
shows the output currents where the regulator’s output voltage drops below 4.75 V. These currents
are close to the limits of the regulator’s capability and generally cannot be sustained for long periods;
under typical operating conditions, a safe limit for the maximum continuous regulator output current is
60% to 70% of the values shown in the graph.
The dropout voltage of a step-down regulator is defined as the minimum amount by which the input
voltage much exceed the regulator’s target output voltage in order to assure the target output can
be achieved. As can be seen in the graph below, the dropout voltage of the Robot Controller SV’s
regulator increases approximately linearly with the output current. For light loads where the dropout
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voltage is small, the board can operate almost down to 5 V. However, for larger loads, the dropout
voltage should be taken into consideration when selecting a power supply; operating above 6 V will
ensure the full output current is available.
Typical dropout voltage of the 5 V regulatoron the A-Star 32U4 Robot Controller SV with
Raspberry Pi Bridge.
Note: Although the MP4423H is rated for a maximum operating input voltage of 36 V, it is
not appropriate to power the Robot Controller SV with a 36 V battery, as battery voltages
can be much higher than nominal voltages when they are charged. The maximum nominal
battery voltage we recommend is 24 V, and if you approach that limit, you should take extra
precautions to prevent LC voltage spikes from damaging the board (see this application
note [https://www.pololu.com/docs/0J16] for more information). A good practice is to ensure that
the A-Star’s power switch is off before connecting it to a voltage source.
3.8. Raspberry Pi interface and level shifters
The A-Star 32U4 Robot Controller with Raspberry Pi Bridge can be used as an expansion board
on top of a Raspberry Pi single-board computer. It conforms to the Raspberry Pi HAT (Hardware
Attached on Top) specification and is designed to connect to the Model B+ and newer versions of the
Raspberry Pi with 40-pin GPIO headers (including the Raspberry Pi 3 Model B [https://www.pololu.com/
product/2759] and Model A+ [https://www.pololu.com/product/2760]). A 2×20-pin 0.1″ female header
[https://www.pololu.com/product/1037] is soldered to the assembled version of the robot controller, and
it ships with a set of four standoffs [https://www.pololu.com/product/1952], screws [https://www.pololu.com/
product/1968], and nuts [https://www.pololu.com/product/1967]. (The header and mounting hardware are
not included with the SMT-only version, but you can solder in either a standard or stackable
[https://www.pololu.com/product/2748] header yourself.)
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I²C communication
When used as a Raspberry Pi add-on, the A-Star is designed to serve as an auxiliary controller,
communicating with the Raspberry Pi using an I²C interface (also known as 2-wire Serial Interface,
or TWI). As such, the ATmega32U4 microcontroller’s I²C data and clock lines (SDA and SCL) are
connected to the corresponding lines on the Raspberry Pi’s I²C bus 1 through on-board level-shifting
circuits. These bidirectional level shifters convert between the AVR’s 5 V logic level and the Raspberry
Pi’s 3.3 V logic level.
We have written an Arduino library [https://github.com/pololu/pololu-rpi-slave-arduino-library] for the robot
controller that lets it act as an I²C slave and provides a framework for communication between
the A-Star and a Raspberry Pi master. A tutorial [https://www.pololu.com/blog/577] on the Pololu blog
demonstrates this library and its included example code, using them to make a robot that can be
remotely controlled and monitored through a web server running on the Raspberry Pi.
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Raspberry Pi robot using the A-Star 32U4 Robot Controller.
General-purpose level shifters
In addition to the dedicated I²C level shifters, the A-Star board also makes available a few general-
purpose level shifters that are not connected to any signals by default.
LS1 is a dual-channel unidirectional level shifter that converts a pair of 5 V inputs (HA and HB) to a
pair of corresponding 3.3 V outputs (LA and LB).
LS2 and LS3 are each single-channel, tristatable, unidirectional level shifters. Each of these exposes
four pins: OE (output enable), IN (input), OUT (shifted output), and VCC (logic supply voltage).
• When OE is high, OUT is in a high impedance state.
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• When OE is low, OUT matches the state of IN, shifted to the voltage supplied on VCC.
For example, if you pull OE low, connect a 3.3 V signal to IN, and connect 5V to VCC, the signal will
be shifted to 5 V logic level on OUT.
The input logic level can be 1.8 V to 5.5 V, while VCC (and the output logic level) can be 3 V to 5.5 V.
The IN signal can have either a lower or higher logic level than the VCC voltage: you could connect a
5 V signal to IN and a 3.3 V to VCC or a 3.3 V signal to IN and a 5 V to VCC.
Powering the Raspberry Pi from the robot controller
The robot controller will provide 5 V power to an attached Raspberry Pi by default, and 3.3 V from the
Raspberry Pi will be used to supply some of the level shifters. See Section 3.5 for more details about
how power is shared and can be controlled between the two boards.
ID EEPROM
The A-Star board includes a 32-kilobit (4096-byte) EEPROM that connects to the Raspberry Pi’s
ID_SD and ID_SC pins. The EEPROM ships with its contents blank, but you can program it as
an ID EEPROM in the format specified by the Raspberry Pi HAT specifications [https://github.com/
raspberrypi/hats], using the utilities provided there. When suitably programmed, the EEPROM can help
the Raspberry Pi identify and configure itself to work with the add-on board.
Write protection for the EEPROM can be enabled by using solder to bridge the surface-mount jumper
labeled “WP” next to the EEPROM chip. (The EEPROM is not write-protected by default.)
3.9. Pinout
These diagrams identify the I/O and power pins on the A-Star 32U4 Robot Controller with Raspberry Pi
Bridge (LV and SV versions); they are also available (along with the power distribution diagram below)
as a printable PDF [https://www.pololu.com/file/0J951/a-star-32u4-robot-controller-with-raspberry-pi-bridge-
pinout-power.pdf] (8MB pdf). For more information about the ATmega32U4 microcontroller and its
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peripherals, see Atmel’s ATmega32U4 documentation.
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Printed on the A* circuit board are indicators that you can use to quickly identify each AVR I/O pin’s
capabilities: an analog pin number (prefixed by the letter A) means the pin can be used as an analog
input, and a square wave symbol next to the hole pair means the pin can be used as a PWM output.
Pin numbers printed as inverted text surrounded by a white box indicate that the pin is used by on-
board hardware (see Section 3.10 for more information about pin assignments).
Additional rows of power and ground pins run along the I/O pins to allow easy connections for devices
like sensors and servos. The outermost row of pins is connnected to ground, and the middle row is
intended for power connections, but not connected by default. The power pins are split into four buses:
two buses along the top, split between digital pins 7 and 8, and two buses along the bottom, split
between AREF and PD5. You can configure each bus separately by using a jumper to connect it to a
voltage source of your choice. (Access points for various supply voltages are available nearby.)
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3.10. Pin assignments
The table below lists the most important pin assignments for the ATmega32U4 on the A-Star 32U4
Robot Controller with Raspberry Pi Bridge. This table is helpful if you want to add your own electronics
to the robot controller, write your own low-level code for interfacing with the hardware, or just want to
understand better how the A-Star works. Each row represents a physical pin on the ATmega32U4.
The “ATmega32U4 pin name” column shows the official name of the pin according to the
ATmega32U4 datasheet [https://www.microchip.com/wwwproducts/en/ATmega32u4].
The “Arduino pin names” column lists the names provided by the Arduino environment for the pin.
These names can generally be used as arguments to any function that takes a pin number. However,
there are some exceptions. For example, passing the number 4 to analogRead actually reads pin A4,
not pin 4. Also, due to hardware limitations, some functions only work on a limited set of pins.
The “A-Star 32U4 Robot Controller functions” column documents what the pin is used for on the A-
Star 32U4 Robot Controller. Many pins can serve multiple purposes concurrently by switching modes.
For example, PB0 can read the state of button C when it is an input, and it can control the red LED
when it is an output.
The “Notes/alternate functions” column documents other features of the pin, although some of those
features might be impractical to use.
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ATmega32U4
pin name
Arduino
pin names
A-Star 32U4 Robot Controller
functionsNotes/alternate functions
PB3 14, MISO User pushbutton A
SPI Master Input/Slave Output (MISO)
Pin-change interrupt (PCINT3)
ISP programming line (PDO)
PB0 17, SSRed LED (RX)
User pushbutton C
SPI slave select (SS)
Pin-change interrupt (PCINT0)
PC7 13 Yellow LED
Timer4 PWM output A (OC4A)
Timer3 input capture pin (ICP3)
Divided system clock output (CLKO)
PD5 -Green LED (TX)
User pushbutton B
UART external clock (XCK1)
UART flow control (CTS)
PD6 12, A11, 29 Motor 1 direction
Analog input (ADC9)
Timer4 PWM output D (OC4D)
Timer1 counter source (T1)
PB5 9, A9, 27 Motor 1 PWM
Analog input (ADC12)
Timer1 PWM output A (OC1A)
Timer4 PWM output B (OC4B)
Pin-change interrupt (PCINT5)
PE2 - Motor 2 direction Hardware bootloader select (HWB)
PB610, A10,
28Motor 2 PWM
Analog input (ADC13)
Timer1 PWM output B (OC1B)
Timer4 PWM output B (OC4B)
Pin-change interrupt (PCINT6)
PD0 3, SCLI²C clock for Raspberry Pi
communication
Timer0 PWM output B (OC0B)
External interrupt source (INT0)
PD1 2, SDA I²C data for Raspberry Pi communication External interrupt source (INT1)
PD7 6, A7, 25Free I/O
Jumper to buzzer PWM
Analog input (ADC10)
Timer4 PWM output D (OC4D)
Timer0 counter source (T0)
PF6 A1, 19Free I/O
Jumper to battery level input (VIN/3)
Analog input (ADC6)
JTAG test data out (TDO)
PD2 0 Free I/OUART receive pin (RXD1)
External interrupt source (INT2)
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ATmega32U4
pin name
Arduino
pin names
A-Star 32U4 Robot Controller
functionsNotes/alternate functions
PD3 1 Free I/OUART transmit pin (TXD1)
External interrupt source (INT3)
PD4 4, A6, 24 Free I/OAnalog input (ADC8)
Timer1 input capture pin (ICP1)
PC6 5 Free I/OTimer3 PWM output A (OC3A)
Timer4 PWM output A (OC4A)
PE6 7 Free I/O
Analog comparator negative input
(AIN0)
External interrupt source (INT6)
PB4 8, A8, 26 Free I/OAnalog input (ADC11)
Pin-change interrupt (PCINT4)
PB7 11 Free I/O
Timer0 PWM output A (OC0A)
Timer1 PWM output C (OC1C)
UART flow control (RTS)
Pin-change interrupt (PCINT7)
PB1 15, SCK Free I/O
SPI Clock (SCK)
Pin-change interrupt (PCINT1)
ISP programming line (SCK)
PB2 16, MOSI Free I/O
SPI Master Output/Slave Input (MOSI)
Pin-change interrupt (PCINT2)
ISP programming line (PDI)
PF7 A0, 18 Free I/OAnalog input (ADC7)
JTAG test data in (TDI)
PF5 A2, 20 Free I/OAnalog input (ADC5)
JTAG test mode select (TMS)
PF4 A3, 21 Free I/OAnalog input (ADC4)
JTAG test clock (TCK)
PF1 A4, 22 Free I/O Analog input (ADC1)
PF0 A5, 23 Free I/O Analog input (ADC0)
RESET - Reset pushbutton internally pulled high, active low
AREF - - Analog reference
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3.11. AVR Timers
The ATmega32U4 has 4 timers: Timer0, Timer1, Timer3, and Timer4. Each timer has a different set of
features, as documented in the datasheet.
• Timer0 is used by the Arduino environment for timing-related functions like millis() .
• Timer1 is used by the A-Star 32U4 Arduino library for driving motors.
• Timer3 is not used by the A-Star 32U4 Arduino library and can be freely used for your own
purposes.
• Timer4 is used by the A-Star 32U4 Arduino library for controlling the buzzer. The Buzzer pin
must be connected to the adjacent digital pin 6 (PD7; Timer4 output OC4D) for this to work.
3.12. Schematics and dimensions
Schematics
The schematic diagrams for the A-Star 32U4 Robot Controllers with Raspberry Pi Bridge are available
as PDFs:
• A-Star 32U4 Robot Controller LV with Raspberry Pi Bridge schematic diagram
[https://www.pololu.com/file/0J950/a-star-32u4-robot-controller-lv-with-raspberry-pi-bridge-schematic.pdf]
(382k pdf)
• A-Star 32U4 Robot Controller SV with Raspberry Pi Bridge schematic diagram
[https://www.pololu.com/file/0J1112/a-star-32u4-robot-controller-sv-with-raspberry-pi-bridge-schematic.pdf]
(427k pdf)
Dimensions
Dimension diagrams for the A-Star 32U4 Robot Controller are available as PDFs:
• A-Star 32U4 Robot Controller LV with Raspberry Pi Bridge dimension diagram
[https://www.pololu.com/file/0J1123/a-star-32u4-robot-controller-lv-with-raspberry-pi-bridge-dimension-
diagram.pdf] (2MB pdf)
• A-Star 32U4 Robot Controller SV with Raspberry Pi Bridge dimension diagram
[https://www.pololu.com/file/0J1118/a-star-32u4-robot-controller-sv-with-raspberry-pi-bridge-dimension-
diagram.pdf] (2MB pdf)
DXF files for each version of the A-Star 32U4 Robot Controller, which show the main board outline
along with the sizes and locations of all of the holes on the board are also available:
• A-Star 32U4 Robot Controller LV with Raspberry Pi Bridge drill guide
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[https://www.pololu.com/file/0J1121/ac04b-drill.dxf] (188k dxf)
• A-Star 32U4 Robot Controller SV with Raspberry Pi Bridge drill guide
[https://www.pololu.com/file/0J1122/ac04c-drill.dxf] (197k dxf)
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4. Getting started
4.1. Installing Windows drivers
If you use Windows XP, you will need to have either Service Pack 3 or Hotfix KB918365
installed before installing the A-Star drivers. Some users who installed the hotfix have
reported problems that were solved by upgrading to Service Pack 3, so we recommend
Service Pack 3 over the hotfix.
Before you connect your Pololu A-Star 32U4 (or another of our 32U4 family of boards) to a computer
running Microsoft Windows, you should install its drivers:
1. Download the A-Star Windows Drivers [https://www.pololu.com/file/0J1240/a-star-
windows-1.3.0.0.zip] (7k zip) and extract the ZIP file to a temporary folder on your computer.
(These files are also available in the “drivers” directory from the A-Star repository on
GitHub [https://github.com/pololu/a-star].)
2. Open the “a-star-windows” folder. Right-click on “a-star.inf” and select “Install”.
3. Windows will ask you whether you want to install the drivers. Click “Install” (Windows 10, 8,
7, and Vista) or “Continue Anyway” (Windows XP).
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4. Windows will not tell you when the installation is complete, but it should be done after a few
seconds.
Windows 10, Windows 8, Windows 7, and Windows Vista users: After installing the drivers, your
computer should automatically recognize the device when you connect it via USB. No further action
from you is required. However, the first time you connect an A-Star device to your computer, Windows
will take several seconds to recognize the device and configure itself properly. The first time you
program the device, Windows will again take several seconds to recognize the A-Star USB bootloader,
and this could cause the programming operation to fail the first time. Also, Windows will need to re-
recognize the device and the bootloader if you connect the board to another USB port that it has not
been connected to before.
Windows XP users: After installing the drivers, you will need to follow steps 5–9 for each new A-Star
device you connect to your computer. You will also need to follow these steps the first time you attempt
to program the device in order to make Windows recognize the bootloader, and when you connect the
device to a different USB port that it has not been connected to before.
5. Connect the device to your computer’s USB port.
6. When the “Found New Hardware Wizard” is displayed, select “No, not this time” and click
“Next”.
7. On the second screen of the “Found New Hardware Wizard”, select “Install the software
automatically” and click “Next”.
8. Windows XP will warn you again that the driver has not been tested by Microsoft and
recommend that you stop the installation. Click “Continue Anyway”.
9. When you have finished the “Found New Hardware Wizard”, click “Finish”.
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Programming the A-Star 32U4 from theArduino IDE.
COM port details
After installing the drivers and plugging in an A-Star, in the “Ports (COM & LPT)” category of the Device
Manager, you should see a COM port for the A-Star’s running sketch named “Pololu A-Star 32U4”.
You might see that the COM port is named “USB Serial Device” in the Device Manager instead of
having a descriptive name. This can happen if you are using Windows 10 or later and you plugged
the A-Star into your computer before installing our drivers for it. In that case, Windows will set up your
A-Star using the default Windows serial driver (usbser.inf), and it will display “USB Serial Device” as
the name for the port. The port will still be usable, but it will be hard to tell if it is the right one because
of the generic name shown in the Device Manager. We recommend fixing the names in the Device
Manager by right-clicking on each “USB Serial Device” entry, selecting “Update Driver Software…”,
and then selecting “Search automatically for updated driver software”. Windows should find the drivers
you already installed, which contain the correct name for the port.
If you are using Windows 10 or later and choose not to install the drivers, the A-Star will still be
usable. To tell which “USB Serial Device” in your Device Manager is the A-Star, double-click on each
one and look at the “Hardware Ids” property in the “Details” tab. An A-Star running a sketch will
have the ID USB\VID_1FFB&PID_2300&MI_00 , while an A-Star in bootloader mode will have the ID USB\
VID_1FFB&PID_0101 .
If you want to change the COM port numbers assigned to your A-Star, you can do so using the Device
Manager. Double-click a COM port to open its properties dialog, and click the “Advanced…” button in
the “Port Settings” tab.
4.2. Programming using the Arduino IDE
Our 32U4 family of boards can be programmed from the
popular Arduino integrated development environment
(IDE). The Arduino IDE is a cross-platform, open source
application that integrates a C++ code editor, the GNU
C++ compiler, and a program upload utility. To get started
programming your device with the Arduino IDE (version
1.6.4 or later), follow these steps:
Download the Arduino IDE from the Arduino Download
page [http://arduino.cc/en/Main/Software], install it, and start
it.
1. In the Arduino IDE, open the File menu
(Windows/Linux) or the Arduino menu
(macOS) and select “Preferences”.
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2. In the Preferences dialog, find the “Additional Boards Manager URLs” text box (highlighted in
the picture below). Copy and paste the following URL into this box:
https://files.pololu.com/arduino/package_pololu_index.json
If there are already other URLs in the box, you can either add this one separated by a comma
or click the button next to the box to open an input dialog where you can add the URL on a
new line.
Adding a Boards Manager index for Pololu boards in the Arduino IDE’s Preferences dialog.
3. Click the “OK” button to close the Preferences dialog.
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4. In the Tools > Board menu, select “Boards Manager…” (at the top of the menu).
5. In the Boards Manager dialog, search for “Pololu A-Star Boards”.
6. Select the “Pololu A-Star Boards” entry in the list, and click the “Install” button.
7. After the installation finishes, click the “Close” button to close the Boards Manager dialog.
8. In the Tools > Board menu, select the “Pololu A-Star 32U4” entry. If you do not see your
device listed in the Board menu, try restarting the Arduino IDE.
Selecting the Pololu A-Star 32U4 in the Boards menu.
9. In the Tools > Port menu, select the port for the device. On Windows you can determine
what COM port the device is assigned to by looking at the “Ports (COM & LPT)” section of
the Device Manager. On Linux, the port name will begin with “/dev/ttyACM”. On Mac OS X,
the port name will begin with “/dev/tty.usbmodem”.
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Windows 10 Device Manager showing the A-Star’s virtual COM port.
10. Open up the “Blink” Arduino example, which can be found under File > Examples >
01.Basics > Blink. The code in this example will blink the yellow LED. When you select the
Blink example, a new Arduino IDE window will open up. It is OK to close the first window.
Selecting the Blink example in the Arduino IDE.
11. Press the “Upload” button to compile the sketch and upload it to the device. If everything goes
correctly, you will see the message “Done uploading” appear near the bottom of the window.
If you are using Windows and you have not previously programmed an A-Star device on this
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USB port, then Windows might take several seconds to recognize the A-Star bootloader. The
bootloader times out after 8 seconds and goes back to running the sketch, so the upload
might fail if Windows does not recognize it quickly enough. If this happens, try again. If you
are using Windows XP and have not programmed an A-Star on this USB port, you will have to
go through the Found New Hardware Wizard again as described in the previous section, but
the second time you try to upload it should work. If the Arduino IDE has trouble connecting to
the port or using it, try unplugging the device, closing any programs that might be using the
serial port, restarting the Arduino IDE, and then plugging the device back in.
Uploading a sketch to the A-Star using the Arduino IDE.
12. If you uploaded the Blink sketch, then the yellow LED should be blinking once every two
seconds. However, we ship some A-Stars with that same example already programmed onto
it, so you might not be convinced that anything has changed. Try changing the delay values
in the sketch to something else and uploading again to see if you can change the speed of
Pololu A-Star 32U4 Robot Controller User’s Guide © 2001–2019 Pololu Corporation
4. Getting started Page 36 of 50
the LED.
The A-Star 32U4 boards are similar enough to the Arduino Leonardo that you do not
actually have to install the add-on. If you want to, you can just select the “Arduino
Leonardo” board in the Arduino IDE. Note that if you upload a sketch to the device this
way, your computer will then recognize it as a Leonardo (for example, its entry in the
Windows Device Manager will display “Arduino Leonardo”).
After you succeed in programming your device from the Arduino IDE, there are many resources you
can use to learn more:
• The Arduino IDE has many examples [http://arduino.cc/en/Tutorial/HomePage] that can run on A-
Stars.
• The Arduino website has a Language Reference [http://arduino.cc/en/Reference/HomePage], a
wiki called the The Arduino Playground [http://playground.arduino.cc/], and other resources.
• The A-Star 32U4 boards are similar to the Arduino Leonardo [https://www.pololu.com/product/
2192] and Arduino Micro [https://www.pololu.com/product/2188], so you can search the Internet
for relevant projects that use one of those boards.
• The Related Resources section lists many more resources.
4.3. Programming using avr-gcc and AVRDUDE
This section explains how to program our 32U4 family of boards using the avr-gcc toolchain and
AVRDUDE. This section is intended for advanced users who do not want to use the Arduino IDE as
described in the previous section.
Getting the prerequisites
If you are using Windows, we recommend downloading WinAVR [http://winavr.sourceforge.net/], which
contains the avr-gcc toolchain and a command-line utility called AVRDUDE [http://www.nongnu.org/
avrdude/] that can be used to upload programs to the A-Star bootloader. If the version of GNU Make
that comes with WinAVR crashes on your computer, we recommend using the Pololu version of GNU
Make [https://github.com/pololu/make/releases].
If you are using Mac OS X, we recommend downloading the CrossPack for AVR Development
[http://www.obdev.at/products/crosspack].
If you are using Linux, you will need to install avr-gcc, avr-libc, and AVRDUDE. Ubuntu users can get
the required software by running:
Pololu A-Star 32U4 Robot Controller User’s Guide © 2001–2019 Pololu Corporation
4. Getting started Page 37 of 50
sudo apt-get install gcc-avr avr-libc avrdude
After you have installed the prerequisites, open a command prompt and try running these commands
to make sure all the required utilities are available:
avr-gcc -vavr-objcopy -Vmake -vavrdude
If any of those commands fail, make sure the desired executable is installed on your computer and
make sure that it is in a directory listed in your PATH environment variable.
Compiling an example program
Copy the following code to a file named “main.c”:
In the same folder, create a file named “Makefile” with the following contents:
PORT=\\\\.\\USBSER000MCU=atmega32u4CFLAGS=-g -Wall -mcall-prologues -mmcu=$(MCU) -OsLDFLAGS=-Wl,-gc-sections -Wl,-relaxCC=avr-gccTARGET=mainOBJECT_FILES=main.o
all: $(TARGET).hex
clean:rm -f *.o *.hex *.obj *.hex
%.hex: %.objavr-objcopy -R .eeprom -O ihex $< $@
%.obj: $(OBJECT_FILES)$(CC) $(CFLAGS) $(OBJECT_FILES) $(LDFLAGS) -o $@
program: $(TARGET).hexavrdude -p $(MCU) -c avr109 -P $(PORT) -U flash:w:$(TARGET).hex
Make sure that the PORT variable in the Makefile is set to the name of the device’s virtual serial port.
123456789
101112131415
#define F_CPU 16000000#include <avr/io.h>#include <util/delay.h>
int main(){
DDRC |= (1 << DDC7); // Make pin 13 be an output.while(1){
PORTC |= (1 << PORTC7); // Turn the LED on._delay_ms(500);PORTC &= ~(1 << PORTC7); // Turn the LED off._delay_ms(500);
}}
?
Pololu A-Star 32U4 Robot Controller User’s Guide © 2001–2019 Pololu Corporation
4. Getting started Page 38 of 50
In Windows, \\\\.\\USBSER000 should work if the A-Star is the only USB device connected that is
using the usbser.sys driver, but you can change it to be the actual name of the COM port (e.g. COM13 ).
In a command prompt, navigate to the directory with the Makefile and main.c. If you run the command
make , the code should get compiled and produce a file named “main.hex”.
Programming
To program the A-Star device, you will need to get it into bootloader mode first. One way to do this is
to reset the AVR twice within 750 ms. Most of the boards in our 32U4 family have a reset button that
can be used to reset the board. On any of our 32U4 family of boards, a pushbutton can be connected
between the GND and RST pins to serve as a reset button, or you can use a wire. Once the device is
in bootloader mode, quickly run the command make program to program it. If you wait longer than 8
seconds, the A-Star bootloader will exit and the AVR will go back to running the user program.
Pololu A-Star 32U4 Robot Controller User’s Guide © 2001–2019 Pololu Corporation
4. Getting started Page 39 of 50
5. A-Star 32U4 Arduino libraryThe A-Star 32U4 can be programmed from the Arduino IDE as described in the preceding sections.
To help interface with all the on-board hardware on the A-Star 32U4, we provide the AStar32U4
library. The AStar32U4 library documentation [https://pololu.github.io/a-star-32u4-arduino-library/]
provides detailed information about the library, and the library comes with several example sketches.
If you are using version 1.6.2 or later of the Arduino software (IDE), you can use the Library Manager
to install this library:
1. In the Arduino IDE, open the “Sketch” menu, select “Include Library”, then “Manage
Libraries…”.
2. Search for “AStar32U4”.
3. Click the AStar32U4 entry in the list.
4. Click “Install”.
If this does not work, you can manually install the library:
1. Download the latest release archive from GitHub [https://github.com/pololu/a-star-32u4-arduino-
library] and decompress it.
2. Rename the folder “a-star-32u4-arduino-library-master” to “AStar32U4”.
3. Move the “AStar32U4” folder into the “libraries” directory inside your Arduino sketchbook
directory. You can view your sketchbook location by opening the “File” menu and selecting
“Preferences” in the Arduino IDE. If there is not already a “libraries” folder in that location,
you should make the folder yourself.
4. After installing the library, restart the Arduino IDE.
After you install the AStar32U4 library, you can learn more about it by trying the included example
sketches and by reading the AStar32U4 library documentation [https://pololu.github.io/a-
star-32u4-arduino-library/].
If you are using the A-Star 32U4 Robot Controller as a Raspberry Pi add-on, you might also want to
make use of our Raspberry Pi slave library for Arduino [https://github.com/pololu/pololu-rpi-slave-arduino-
library], which sets up the A-Star as an I²C slave and helps establish communication with a Raspberry
Pi master. See Section 3.8 for more information about the Raspberry Pi interface.
Pololu A-Star 32U4 Robot Controller User’s Guide © 2001–2019 Pololu Corporation
5. A-Star 32U4 Arduino library Page 40 of 50
6. The A-Star 32U4 USB interfaceOur 32U4 family of boards are based on a single AVR ATmega32U4 microcontroller that runs the
user program and also handles the USB connection to the computer. The AVR has a full-speed USB
transceiver built into it and can be programmed to present almost any type of USB device interface to
the computer.
USB is an asymmetric system that consists of a single “host” connected to multiple “devices”. The host
is typically a personal computer. The ATmega32U4 can only act as a USB device, so an A-Star device
cannot be connected to other USB devices like mice and keyboards; it can only be connected to a
host such as your computer.
Programming an ATmega32U4 board using the Arduino IDE as described earlier will automatically
configure it as a composite device with a single virtual serial port. If you program the microcontroller
with an Arduino sketch that implements another USB device class, like HID or MIDI, you will see
additional child devices as well.
On a Windows computer, you can see the virtual serial port by going to your computer’s Device
Manager and expanding the “Ports (COM & LPT)” list. You should see a COM port labeled “Pololu A-
Star 32U4”. In parentheses after the name, you will see the name of the port (e.g. “COM3” or “COM4”).
Windows will assign a different COM port number to the device depending on what USB port you
plug it into and whether it is in bootloader mode or not. If you need to change the COM port number
assigned to the A-Star, you can do so using the Device Manager. Double-click on the COM port to
open its properties dialog, and click the “Advanced…” button in the “Port Settings” tab. From this dialog
you can change the COM port assigned to the device.
Windows 10 Device Manager showing the A-Star’s virtual COM port.
On a Windows computer, you can see the rest of the USB interface by going to the Device Manager,
selecting View > Devices by connection, and then expanding entries until you find the “Pololu A-Star
Pololu A-Star 32U4 Robot Controller User’s Guide © 2001–2019 Pololu Corporation
6. The A-Star 32U4 USB interface Page 41 of 50
32U4” COM port. Near it, you should see the parent composite device.
The Windows 10 Device Manager in “Devices by connection” mode, showingthat the A-Star is a composite device.
On a Linux computer, you can see details about the USB interface by running lsusb -v -d 1ffb: in
a Terminal. The virtual serial port can be found by running ls /dev/ttyACM* in a Terminal.
On a Mac OS X computer, the virtual serial port can be found by running ls /dev/tty.usbmodem* in a
Terminal.
You can send and receive bytes from the virtual serial port using any terminal program that supports
serial ports. Some examples are the Serial Monitor in Arduino IDE, the Pololu Serial Transmitter
Utility [https://www.pololu.com/docs/0J23], Br@y Terminal [http://sites.google.com/site/terminalbpp/], PuTTY
[http://www.chiark.greenend.org.uk/~sgtatham/putty/], TeraTerm [http://ttssh2.sourceforge.jp/], Kermit
[http://www.columbia.edu/kermit/ck80.html], and GNU Screen [http://www.gnu.org/software/screen/]. Many
computer programming environments also support sending and receiving bytes from a serial port.
Pololu A-Star 32U4 Robot Controller User’s Guide © 2001–2019 Pololu Corporation
6. The A-Star 32U4 USB interface Page 42 of 50
7. The A-Star 32U4 BootloaderOur 32U4 family of boards come with a USB bootloader that can be used in conjunction with the
Arduino IDE or AVRDUDE to load new programs onto the device. This section documents some
technical details of the bootloader for advanced users who want to better understand how it works. If
you just want to get started using your device, it is fine to skip this section.
The A-Star 32U4 Bootloader is based on the Caterina bootloader [https://github.com/arduino/Arduino/tree/
master/hardware/arduino/avr/bootloaders/caterina], which is the bootloader used on the Arduino Leonardo
[https://www.pololu.com/product/2192], Arduino Micro [https://www.pololu.com/product/2188] and several other
ATmega32U4 boards. The bootloader is open source and its source code [https://github.com/pololu/
a-star/tree/master/bootloaders/caterina] is available on GitHub. The bootloader occupies the upper four
kilobytes of the ATmega32U4’s program memory, leaving 28 KB for the user program. The
bootloader’s USB interface consists of a single virtual serial port that accepts the programming
commands defined in AVR109 [http://www.atmel.com/images/doc1644.pdf]. The bootloader always runs first
immediately after the AVR is reset.
Startup logic
The main difference between the A-Star 32U4 Bootloader and Caterina is in the startup logic. This
is the part of the bootloader that runs immediately after the AVR is reset, and it decides whether to
run the user program or run the rest of the bootloader. The startup logic of the Caterina bootloader is
designed so that when the RST line goes low, the bootloader will run. This means that if you want to
restart your program using the RST line, it will take 8 seconds before the bootloader times out waiting
for an upload and the sketch starts.
The A-Star 32U4 Bootloader has different startup logic that allows you to use the RST line to reset the
board with a smaller delay. If the RST line goes low once, the user program will run after a 750 ms
delay. If the RST line goes low twice within 750 ms, then the bootloader will run. (This behavior is the
same as on boards like SparkFun’s Pro Micro.)
The start-up logic of the A-Star 32U4 Bootloader is shown in the flowchart below:
Pololu A-Star 32U4 Robot Controller User’s Guide © 2001–2019 Pololu Corporation
7. The A-Star 32U4 Bootloader Page 43 of 50
The startup logic for the A-Star 32U4 bootloader.
Brown-out detection
Unlike many other ATmega32U4 boards, our 32U4 family of boards have brown-out detection enabled.
The brown-out threshold is 4.3 V, and if the voltage on VCC goes below this then the AVR will reset.
Pololu A-Star 32U4 Robot Controller User’s Guide © 2001–2019 Pololu Corporation
7. The A-Star 32U4 Bootloader Page 44 of 50
The bootloader was designed so that the user program can detect brown-out resets. To do so, check
to see if the BORF bit in the MCUSR register is set, and then clear it later. Here is some example code
you could put in your setup function for detecting brown-out resets:
123456789
1011121314
pinMode(13, OUTPUT);if (MCUSR & (1 << BORF)){
// A brownout reset occurred. Blink the LED// quickly for 2 seconds.for(uint8_t i = 0; i < 10; i++){
digitalWrite(13, HIGH);delay(100);digitalWrite(13, LOW);delay(100);
}}MCUSR = 0;
?
Pololu A-Star 32U4 Robot Controller User’s Guide © 2001–2019 Pololu Corporation
7. The A-Star 32U4 Bootloader Page 45 of 50
8. Reviving an unresponsive A-StarIn order to load a new program onto your A-Star 32U4 device, you will need to get it into bootloader
mode and send programming commands to it over its virtual serial port using appropriate software. If
you are programming the device from the Arduino IDE, the sketch loaded onto the device will generally
support a special USB command for putting it in bootloader mode, and the Arduino IDE sends that
command automatically when you click the Upload button. However, you might find yourself in a
situation where the device is unresponsive and that method will not work. This can happen for two
reasons:
• You accidentally loaded a malfunctioning program onto the device that is incapable of
responding to the special USB command. For example, your program might be stuck in an
infinite loop with interrupts disabled.
• You loaded a program which uses a non-standard type of USB interface or no USB interface.
The following sections provide different procedures you can use to revive your device.
8.1. Reviving using the Arduino IDE
This section explains two special methods for programming an A-Star (or another of our 32U4 family
of boards) using the Arduino IDE in case your usual method of programming is not working. These
instructions were developed for the Arduino IDE versions 1.0.5-r2 and 1.6.0, and they might need to
be modified for future versions.
Reset button
If you have an A-Star 32U4 Micro, you should connect a momentary pushbutton
[https://www.pololu.com/product/1400] between the GND and RST pins to serve as a reset button. Other
boards in our 32U4 family have a reset button you can use. Alternatively, you can use a wire to
temporarily connect GND and RST together instead of using a reset button.
Resetting the board twice within 750 ms makes the board go into bootloader mode. The bootloader
will exit after 8 seconds and try to run the sketch again if it has not started receiving programming
commands. To revive the device, you need to make sure you start sending it programming commands
before the 8-second period is over.
In bootloader mode, the yellow LED (the one labeled LED 13) fades in and out. It is useful to look at
this LED so you can know what mode the microcontroller is in. Also, we recommend enabling verbose
output during upload using the Arduino IDE’s “Preferences” dialog. Looking at the LED and looking at
the verbose output during the following procedures will help you understand what is going on.
Pololu A-Star 32U4 Robot Controller User’s Guide © 2001–2019 Pololu Corporation
8. Reviving an unresponsive A-Star Page 46 of 50
The uploading-before-bootloader method
The goal of the uploading-before-bootloader method is to select a non-existent serial port in the
Arduino IDE and then make sure the Arduino IDE enters the uploading phase before the
microcontroller goes into bootloader mode. This method has been tested on Arduino 1.0.5-r2 and
1.6.0. This method does not work on Arduino 1.5.6-r2 because that version of the IDE gives a fatal
error message if the selected serial port is not present at the beginning of the uploading phase (e.g.
“Board at COM7 is not available.”).
1. Connect the device to your computer via USB.
2. In the “Tools” menu, open the “Board” sub-menu, and select “Pololu A-Star 32U4”.
3. In the “Tools” menu, open the “Port” sub-menu, and check to see if any ports are selected. If
the “Port” menu is grayed out or no ports in it are selected, that is good, and you can skip to
step 6.
4. Reset the board twice to get the board into bootloader mode. While the board is in bootloader
mode, quickly select the new serial port that corresponds to the bootloader in the “Port”
menu.
5. After 8 seconds, the bootloader will exit and attempt to run the sketch again. Wait for the
bootloader to exit. Verify that either the “Port” menu is grayed out or no ports in it are selected.
6. Click the Upload button. The Arduino IDE will compile your sketch and start uploading it.
7. As soon as the large status bar near the bottom of the IDE says “Uploading…”, reset the
board twice to get into bootloader mode.
The Arduino IDE will stay in the uploading phase for 10 seconds, waiting for a new serial port to
appear. Once the serial port of the bootloader appears, the Arduino IDE will connect to it and send
programming commands.
The bootloader-before-uploading method
The goal of the bootloader-before-uploading method is to select the bootloader’s virtual serial port in
the Arduino IDE and then make sure the board is in bootloader mode at the time when the Arduino
IDE enters the uploading phase.
1. Connect the device to your computer via USB.
2. In the “Tools” menu, open the “Board” sub-menu and check to see if the “Pololu A-Star 32U4
(bootloader port)” entry is visible. If this entry is visible, you can skip to step 6.
3. If you are using a 1.0.x version of the Arduino IDE, open the file [sketchbook
location]/hardware/pololu/boards.txt using a text editor. If you are using a 1.5.x version
of the Arduino IDE, open the file [sketchbook location]/hardware/pololu/avr/boards.txt
Pololu A-Star 32U4 Robot Controller User’s Guide © 2001–2019 Pololu Corporation
8. Reviving an unresponsive A-Star Page 47 of 50
using a text editor. You can see the sketchbook location in the Arduino IDE preferences
dialog. The file you are looking for is part of the A-Star add-on.
4. In the boards.txt file that you opened, find the lines at the bottom of the file that start with
#a-star32U4bp . Uncomment each of those lines by deleting the “#” character, and then save
the file.
5. Close the Arduino IDE and restart it.
6. In the “Tools” menu, open the “Board” sub-menu and select “Pololu A-Star 32U4 (bootloader
port)”. This entry is configured so that the Arduino IDE will send programming commands
directly to selected serial port, instead of trying to send a special USB command to the port
to get it into bootloader mode and then waiting for the new port to appear. By selecting this
entry, the timing of the programming process below becomes easier, especially on Windows.
7. Prepare the computer to show you a list of its virtual serial ports. If you are using Windows,
this means you should open the Device Manager. If you are on Linux or Mac OS X, this
means you should open a Terminal and type the command ls /dev/tty* but do not press
enter until the board is in bootloader mode in the next step.
8. Reset the board twice to get the board into bootloader mode. While it is in bootloader mode,
quickly look at the list of serial ports provided by your operating system in order to determine
what port the bootloader is assigned to.
9. Reset the board twice to get the board into bootloader mode again. While the board is in
bootloader mode, quickly select the serial port of the bootloader in the Arduino IDE. The port
can be selected in the “Port” sub-menu under “Tools”.
10. In the Arduino IDE, click the “Verify” button to compile your sketch. This could make the timing
easier during the next step.
11. Press the reset button twice to get the board into bootloader mode again. As soon as you
see the yellow LED fading in and out, press the Upload button.
The Arduino IDE will compile your sketch and then upload it to the selected serial port.
If the compilation of the sketch takes longer than 8 seconds, then this procedure will fail because the
bootloader will time out and start trying to run the malfunctioning sketch again. If that happens, try the
procedure again using a simpler sketch such as the Blink example that can be found under File >
Examples > 01.Basics > Blink.
After reviving your device, be sure to change the Board setting back to “Pololu A-Star 32U4” and select
the right Port.
8.2. Reviving using AVRDUDE
This section explains a special method for reviving an A-Star (or another of our 32U4 family of boards)
Pololu A-Star 32U4 Robot Controller User’s Guide © 2001–2019 Pololu Corporation
8. Reviving an unresponsive A-Star Page 48 of 50
using the command-line utility AVRDUDE [http://www.nongnu.org/avrdude/] in case your usual method of
programming is not working. AVRDUDE stands for “AVR Downloader/UploaDEr”, and it is compatible
with the A-Star bootloader.
If you have an A-Star 32U4 Micro, you should connect a momentary pushbutton
[https://www.pololu.com/product/1400] between the GND and RST pins to serve as a reset button. Other
boards in our 32U4 family have a reset button you can use. Alternatively, you can use a wire to
temporarily connect GND and RST together instead of using a reset button.
1. Connect the device to your computer via USB.
2. Prepare the computer to show you a list of its virtual serial ports. If you are using Windows,
this means you should open the Device Manager. If you are on Linux or Mac OS X, this
means you should open a Terminal and type the command ls /dev/tty* but do not press
enter until the board is in bootloader mode in the next step.
3. Press the reset button twice within 750 ms to make the AVR go into bootloader mode. You
should see the yellow LED fading in and out when the AVR is in bootloader mode. While it is
in bootloader mode, quickly look at the list of serial ports provided by your operating system
in order to determine what port the bootloader is assigned to.
4. Type the following command in your terminal and replace COM4 with the name of the
bootloader’s serial port, but do not press enter yet. This command will erase the
malfunctioning program on the device but preserve the bootloader.
avrdude -c avr109 -p atmega32U4 -P COM4 -e
5. Press the reset button twice within 750 ms to make the AVR go into bootloader mode.
6. Quickly run the command you typed previously. The command needs to be run within
8 seconds of starting the bootloader, or else the bootloader will exit and try to run the
malfunctioning program again.
By following the instructions above, the malfunctioning program on the device will be erased and the
device will stay in bootloader mode indefinitely. You can now load another program onto it using the
Arduino IDE or AVRDUDE.
Pololu A-Star 32U4 Robot Controller User’s Guide © 2001–2019 Pololu Corporation
8. Reviving an unresponsive A-Star Page 49 of 50
9. Related resourcesTo learn more about using the Pololu A-Star boards, see the following list of resources:
• The Arduino IDE has many examples [http://arduino.cc/en/Tutorial/HomePage] that can run on the
A-Stars.
• The Arduino website has a Language Reference [http://arduino.cc/en/Reference/HomePage], a
wiki called the The Arduino Playground [http://playground.arduino.cc/], and other resources.
• The A-Star boards are similar to the Arduino Leonardo [https://www.pololu.com/product/2192]
and Arduino Micro [https://www.pololu.com/product/2188], so you can search the Internet for
relevant projects that use one of those boards.
• Atmel’s ATmega32U4 documentation [https://www.microchip.com/wwwproducts/en/ATmega32u4]
has the ATmega32U4 datasheet and many related documents.
• AVR Libc Home Page [http://www.nongnu.org/avr-libc/]: this page documents the standard
library of functions that you can use with GNU C and C++ compilers for the AVR.
• A-Star 32U4 Arduino library [https://github.com/pololu/a-star-32u4-arduino-library]
• AStar32U4 library documentation [https://pololu.github.io/a-star-32u4-arduino-library/]
• LUFA – the Lightweight USB Framework for AVRs [http://www.fourwalledcubicle.com/
LUFA.php]
• WinAVR [http://winavr.sourceforge.net/]
• Atmel Studio 7 [https://www.microchip.com/avr-support/atmel-studio-7]
• AVRDUDE [http://www.nongnu.org/avrdude/]
• AVR Freaks [http://www.avrfreaks.net/]
Datasheets for some of the components found on the A-Star 32U4 boards are available below (not all
components apply to every board):
• Texas Instruments TPS2113A power multiplexer datasheet [https://www.pololu.com/file/
0J771/tps2113a.pdf] (1MB pdf)
• Texas Instruments DRV8838 motor driver datasheet [https://www.pololu.com/file/0J806/
drv8838.pdf] (1MB pdf)
• Maxim MAX14870 motor driver datasheet [https://www.pololu.com/file/0J885/MAX14870.pdf]
(492k pdf)
Finally, we would like to hear your comments and questions on the A-Star section of the Pololu
Robotics Forum [http://forum.pololu.com/viewforum.php?f=10]!
Pololu A-Star 32U4 Robot Controller User’s Guide © 2001–2019 Pololu Corporation
9. Related resources Page 50 of 50
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